International Scientific Journals
of Scientific Technical Union of Mechanical Engineering "Industry 4.0"

The industrial concrete floorings of a large warehouse for storing various bulk fertilizer substances in the Varna region are made as hybrid fiber-reinforced one by using a high-quality powdered surface hardener (dry shake topping) to increase their surface hardness and abrasive resistance. The floors are sized and constructed to take on the specific operational loads – a bulk uniform distributed load with a large mass and a mobile front-end loader with a metal rake. Given the expected possible corrosion effect of pre-specified heterogeneous fertilizer substances in the working concrete mix design is used sulfate-resistant cement, which should ensure defect-free operation. Regardless of the measures taken after one year of operation, the presence of surface defects on the floor in strictly limited areas of operation is reported. A reasonable question arises as to the reasons for this. The report discusses an innovative experimental-theoretical approach proposed by the author to identify the causes of this defect with the combined use of a complex method based on the combine use of standardized mechanical and structural direct physical methods of investigation. After specialized sampling and examination of the concrete strength in specific areas, as well as after additional application of X-ray structural and differential thermal analysis, as well as scanning electron microscopy, original scientific results were obtained, which revealed the causes and mechanism of the discussed corrosion damage, and these complex activities definitely have a justified arbitration significance.

Activated carbon derived from polystyrene waste was evaluated as an adsorbent for the removal of the reactive dye Drimaren Red K-7B from aqueous solutions at different temperatures. The adsorption equilibrium was analyzed using Langmuir, Freundlich and Dubinin-Radushkevich models, with the latter providing the best fit (R²=0.97). Kinetic data followed the pseudo-second-order model at all temperatures (R²=0.99). The maximum adsorption capacity reached 35 mg/g at 20 °C. Thermodynamic analysis revealed negative Gibbs free energy values, confirming the spontaneous nature of the process, while positive enthalpy and entropy indicated an endothermic mechanism accompanied by increased interfacial disorder. These results demonstrate the potential of polystyrene-derived activated carbon as an efficient adsorbent for water treatment applications.

Galvanized steel pipes have long been widely used in drinking water supply systems due to the zinc coating that protects the steel from corrosion. However, during operation, especially when hot water is supplied, the zinc protective layer gradually breaks down, especially if there are galvanic pores in the pipeline or stray electric currents are generated in the pipeline. If the zinc coating is damaged, the steel base begins to corrode, rust forms, the pipe wall thickness decreases and the water quality deteriorate.
In addition to internal corrosion, a significant problem is external pipe corrosion caused by condensation forming on the surface of cold-water pipes. When the pipe surface temperature is below the dew point of the ambient air, moisture accumulates on it. Long-term wetting of the surface, especially if the zinc coating or protective paint layer is damaged, creates favorable conditions for the development of atmospheric corrosion. The corrosion process is further accelerated by poor indoor ventilation, high relative humidity or incorrectly calculated insulation layer thickness.
The article will examine two corrosion situations of steel pipes for drinking water supply using metallographic, water parameter studies, and stray current measurements.

Welding is a complex process governed by a multitude of factors. Additive manufacturing and Industry 4.0 or 5.0 require the acquisition of specific knowledge related to closed-loop welding processes, supported by highly qualified personnel. The shortage of specialized personnel within the EU is being addressed through the launch of innovative research projects in support of multidisciplinary and multinational consortia. Through consensus, these consortia develop curricula, courses, and evaluation criteria. These materials are disseminated to those interested in specializing as trainers of specialists or process operators, through platforms that are easy to access and use for self-training and for obtaining certificates that confirm the knowledge acquired. These self-training methods are accompanied by the creation of regional centers of excellence and by the launch of innovative ideas for practical implementation, including the creation of start-ups based on the knowledge acquired.

The article deals with the assessment of the suitability of the manufacturing process and the analysis of the gear runout. The measurements were carried out using the 3D measuring device Wenzel WGT 280. The Palstat CAQ software was used to evaluate the process, while control charts for individual values and the sliding range were applied. The average value of the process reached 0.1460 and the sliding range was 0.00409. The suitability of the process was assessed using the Cp and Cpk indices with a required value ≥ 1.33, while the calculated values were 1.47 and 1.34. The results confirm that the monitored process is suitable. Subsequently, a comparison of the runout before and after heat treatment – nitriding was performed. The specified tolerance limits (0 μm to 0.0320 μm) were not exceeded, which confirmed the satisfactory state of the process even after the treatment.

Features of modeling multilayer metal cord structures are shown. Data on the parameters of the numerical model of metal cord twisting and stretching are given. The dependences of the magnitude of stresses during the destruction of metal cord on the diameter of wires for various metal cord structures are determined. It is shown that symmetrical steel cord structures are less susceptible to a decrease in aggregate strength. The difference between the breaking forces of a multilayer symmetric metal cord with a core is about 10%. It is shown that with an increase in the wire diameter, there is no significant increase in the fracture stresses.

This work is devoted to the development and research of a new technology for processing bar scrap from 40X steel to obtain high-quality finished metal products in the form of a screw reinforcement profile. The developed technology included two stages. At the first stage, the round-section bar scrap is formed on a radial-shear rolling mill to obtain conventional bars of the desired diameter and create initial conditions for the formation of an ultrafine grained gradient structure in the resulting screw profile. The second stage is the direct production of a screw profile with a gradient ultrafine-grained structure on a combined installation. Metallographic studies have shown that after the implementation of the second stage of obtaining a screw reinforcement profile, a gradient structure is observed in 40X steel, with equiaxed grains, the size of which lies within 1.2-1.4 μm in the peripheral region and to a greater extent with elongated, directional-oriented grains in the central region of the resulting reinforcement.

This paper presents the results of studies on the thermophysical and sound-insulating properties of new composite materials intended for interior and exterior plasters in construction. The materials were developed on the basis of foam glass granules and thermally treated rice husks using a specialized methodology. The guarded hot plate method was used to investigate the thermal insulation properties of the composite plasters. Tests for determining the acoustic insulation characteristics were carried out under laboratory conditions using the two-chamber method. The results show that the newly developed composite plasters exhibit better thermal and acoustic insulation properties than the standard plaster compositions traditionally used in construction.

A method for automatic quality control of blanked parts based on the ratio of the plastic deformation (shear) zone to the brittle fracture (rupture) zone on the cut surface is presented. Unlike known approaches that require strictly controlled shooting conditions, the proposed convolutional AI model (R-CNN) demonstrates robustness to a wide range of illumination: variations in brightness and light incidence angle reduce segmentation accuracy by no more than 3%. This is achieved through the use of local texture features that are invariant to brightness scale. The system takes into account the material grade — reference ratios of the zones are defined for each steel grade. Experiments were carried out on samples of three grades (AISI 1010, S235JR, AISI 1066). The classification accuracy of acceptable and defective parts was 98% relative to expert assessment.

This article presents a study of the possibility of creating adhesive-mechanical bonds between aluminum and a thermoplastic matrix composite. In detail, the influence of drilling process parameters on the shape of the bushing and the formation of joints with fiber-reinforced composites during direct drilling using various tool speeds and feeds is examined. Finally, the load-bearing capacity of the formed joints is presented.

In plastic injection and plastic welding processes, the inability to accurately classify machine downtimes, the lack of visibility regarding performance discrepancies between shifts, and the reliance on largely manual methods for operator tracking hinder the sustainable improvement of Overall Equipment Effectiveness (OEE). Furthermore, the retention of pro- duction and energy consumption data in isolated systems complicates integrated performance evaluation.
In this study, the HBS MES system, developed by the in-house engineering team of Pleksan A.S. and fully integrated with HBS ERP, is examined within the scope of a field application aimed at real-time production tracking, performance analysis, and energy consumption reporting in plastic injection lines. As of 2025, HBS MES is actively used in its V1 version across three different plastic manufacturing enterprises; this paper exemplifies a facility predominantly focused on plastic injection.
The paper presents the system architecture, data collection logic, modeling of production and downtime events, the approach to calculating OEE and its sub-metrics, and user interface components in detail. As a result of the implementation in the studied facility, an improvement of approximately 25% in production quantities was reported, particularly during night shifts, and the mechanisms underlying this improvement are discussed. The findings demonstrate that MES solutions integrated with machine-embedded data collection modules can provide measurable productivity gains even in small and medium-sized enterprises.

At the start of exploitation of any hydrocarbon or geothermal water reservoir, production of reservoir fluids is driven by natural energy in the form of reservoir pressure. Therefore, the primary task for production engineers is to maintain this reservoir pressure for as long as possible, ensuring long-term economic production. Unfortunately, sooner or later it becomes necessary to introduce mechanical methods of fluid lifting. Today, there are numerous solutions on the market for mechanical lifting of reservoir fluids (progressing cavity pumps-PCP, electric submersible pumps-ESP), and one of the oldest mechanical methods for producing reservoir fluids is the sucker rod pump. In the Republic of Croatia, sucker rod pumps are among the most commonly used mechanical methods for lifting reservoir fluids. Although Croatian production engineers have significant experience working with sucker rod pumps, operational problems are common and are accompanied by additional expenses related to workover operations. This paper presents an analysis of workover operations over a tenyear period (from 2011 to 2022) in an oil and gas field in the Republic of Croatia. Based on the collected data, an analysis was conducted to determine the volume of fluid not produced during equipment maintenance and repair, the waiting time for repairs, the duration of equipment maintenance as well as the cost-effectiveness of the repairs. Special attention is given to the analysis of the causes of problems in using sucker rod pumps and the identification of problematic wells.